Woven papermaking drainage fabric having four shed weave pattern and weft threads of alternating diameter

ABSTRACT

A papermaking fabric woven from synthetic monofilaments is shown in which the warp threads pass under one and then over three weft threads in a repeated pattern, and the weft threads alternate in diameter to develop a fabric wear surface that is uneven with the average level of the smaller diameter weft threads being receded into the fabric to a greater degree than for the larger weft threads.

United States Patent 1191 Egan 1451 Dec. 3, 1974 22 Filed:

[ 1 WOVEN PAPERMAKING DRAINAGE FABRIC HAVING FOUR SHED WEAVE PATTERN ANDWEFT THREADS OF ALTERNATING DIAMETER 75] Inventor:

[73] Assignee: Albany International Corp.,

Appleton, Wis.

Apr. 18, 1973 [21] Appl. No.: 352,320

Cleon J. Egan, Kaukauna, Wis.

[52] US. Cl 139/420 R, 139/425 A, 162/348, l62/DIG. 1, 245/2, 245/8 [51]Int. Cl. D21f 1/10 [58] Field of Search 162/348, DIG. 1; 139/383 A, 425A, 420 R, 425 A; 245/2, 8

[56] References Cited UNITED STATES PATENTS 1,616,222 2/1927 Harrigan162/DIG. l

lW/I

2,554,034 5/1951 Koester et al 139/383 A 3,216,893 l1/l965 Schuster139/425 x 3,603,354 9/1971 Lee et al 139/383 A 3,681,193 8/1972 Nykopp102/133 x FOREIGN PATENTS OR APPLICATIONS 630,975 11/1961 Canada 139/425A Primary Examiner-Robert L. Lindsay, Jr. Assistant Examiner-Richard H.Tushin Attorney, Agent, or Firm-Quarles & Brady [57] ABSTRACT Apapermaking fabric woven from synthetic monofilaments is shown in whichthe warp threads pass under one and then over three weft threads in arepeated pattern, and the weft threads alternate in diameter to developa fabric wear surface that is uneven with the average level of thesmaller diameter weft threads being receded into the fabric to a greaterdegree than for the larger weft threads.

7 Claims, 4 Drawing Figures PAIENIEL 3.851.681

sum 10? 2 PATENTELBEB 3W 3.851.681. SREEI 28$ 2 BACKGROUND OF THEINVENTION This invention relates to the field of papermaking fabrics,particularly as used on Fourdrinier machines.

In the manufacture of paper on a Fourdrinier machine a slurry of paperpulp is laid down on a large, moving belt in the form of a woven openmesh fabric. Water is drained from the pulp through the fabric to formthe pulp fibers into an initial paper web, which web is then transferredfrom the Fourdrinier machine to the dryer section of the papermakingapparatus.

Fourdrinier fabrics have been woven in a variety of weave patterns andfrom a large selection of materials. For many years they were woven frommetal wire with soft brass for the recessed weft threads and bronzes forthe warp threads which were exposed at their knuckles on the wear sideto take the primary wear. Other metals including stainless steel havebeen employed, and both single and multiple strands as well as hollowwires have been woven into Fourdrinier fabrics. Weave patterns haveconsisted of plane weaves, semi-twill weaves, and a variety of four shedweaves. In recent years synthetic materials have been introduced intothe art, and at times they have been intermixed with metal threads.Also, there has been some use of synthetic coated metal wires.

Synthetic threads can be selected from a variety of materials. Some ofthe earlier work used nylon for its abrasive resistant characteristics,but there has been a shift to polyesters which are nearly non-waterabsorbent and generally inert to paper pulp slurries. Both monofilamentand multi-strand synthetic threads have been used. One of the problemswith synthetic materials is that they do not take a permanent set, as dometal threads, when crimped in the weaving process, and a variety oftreating techniques have been developed to dimensionally stabilize thesynthetic fabrics after weaving.

A Fourdrinier fabric must satisfy a number of requirements in order tobe suitable for papermaking. It must present a smooth surface on itsupper or papermaking side, in spite of the open mesh characteristic, sothat the resulting paper web will not carry wire marking from thefabric. It must have proper water drainage rates and retain the finerpulp fibers on the surface, rather than to lose them in the drainingwater. It must function as a web forming medium in which paper fibersbecome intertwined with an adequate percentage in the cross machinedirection. The under, or wear side should not groove suction boxes,machine rolls or foils. A fabric must also have adequate tensilestrength to be drawn around and over the machine rolls at high speeds,and it should be dimensionally stable, without excessive stretch.Further, a fabric should lie smooth and not buckle or warp in any of itssurface regions. The fabric should be woven in such a manner thatadequate seams with requisite life and strength can be used to join thefabric ends into an endless belt.

A particular objective is to provide a fabric that will have a longlife, for the down time involved in installing and removing fabrics on aFourdrinier machine is very costly. Metal fabrics had lives measured indays, and synthetic materials have lasted, in contrast, for weeks andmonths. Hence, there has been a shift in the industry from the metal tothe synthetic materials. Longer life has been the result of enhancedabrasion resistance and less wear from passing over suction boxes,machine rolls and foils. Also, the chemical inertness and resistance tocorrosion has been a factor favoring synthetic materials.

In meeting the foregoing variety of requirements, I

each fabric must also be compatible with, and tailored for theparticular papermaking machine on which it is to be used. Hence, resultsof weaves, patterns and materials successful in one installation may notnecessarily be satisfactory in another application. Also to beconsidered is the fineness of the fabric mesh. Some weaves are as coarseas less than 10 warp threads to the inch, whereas other weaves haveseveral hundred warp threads to the inch. Usually the number of weftthreads per inch is somewhat less, but there are notable exceptions tothis generalization.

Into this extensive background of weaving techniques and practices, thepresent invention introduces an uneven surface on the wear side of afabric for the principal purpose of further improving fabric life.

SUMMARY OF THE INVENTION The invention resides in a Fourdrinier fabrichaving weft threads of varying diameter with points along the smallerdiameter wefts being at a different level in the fabric than thecorresponding points of the larger diameter wefts to develop an unevensurface.

It is usual to have all the warp threads of one diameter and all theweft threads of another diameter. By introducing weft threads ofalternating diameter the wear surface is made more uneven than in usualweaves. It may be an anomaly to speak of a fabric surface, when it is anopen mesh and comprised of threads woven into knuckles at cross overpoints, and with the threads following a somewhat sinuous configurationwhich does not define a plane at all. Nonetheless, the term surface isused herein to denote the general contour as seen from one side or theother of the fabric, and the points along a thread are referred to asbeing at levels within the fabric meaning at a level, or height, withinthe maximum thickness of the fabric as measured from the outermostthread knuckle surfaces that define the outermost planes of the fabric.

It is not in of itself novel to use weft threads of varying diameter. InU.S. Pat. No. 3,216,893 this is done, but metal wefts alternate withplastic wefts in a plain weave, i.e., one over-one under, and theplastic weft are the larger in diameter in order to have all warpknuckle crests lie in a single plane on each side of the fabric. Thegoal there is to have a mono-plane on each fabric side that is composedof warp knuckles alone. That is a quite different objective from that ofthe present invention. Reinforcing strands of smaller diameter have beenlaid in a nonwoven relation alongside the warp threads of the selvedgearea in U.S. Pat. No. 3,523,867, and in U.S. Pat. No. 1,616,222 aFourdrinier fabric has larger than normal warp and weft threads atspaced intervals along the fabric to change drainage characteristics fordeveloping water marks in the resulting paper. Neither of thesepractices is similar to the present invention.

In the invention the weft preferably alternate in diameter so thatadjacent threads on one side of the fabric lie at different averagelevels in the fabric. This unevenness of the thread levels within thefabric occurs with the minute spacing of adjacent threads over theentire fabric surface. When this non-uniform surface is used as the wearsurface increased fabric life has resulted. The reason is not fullyunderstood, but it may be surmised that the water flow characteristicsthrough the fabric, particularly the lower part of the fabric that ridesover suction boxes, machine rolls and foils has been modified. Water maymore readily flow along the fabric wear surface and form a film whichlubricates the individual threads to reduce abrasive wear. Or, it may bethat the provision of some larger weft threads introduces larger wearsurface areas which prolong fabric life. Since the exact nature of thephenomena involved is not known, these explanations are not to beconstrued as any limitation in the definition of the invention.

Principal objects of the invention are to provide a Fourdrinier fabricthat is relatively non-uniform on its wear surface, and to achievebetter wear and life characteristics.

The foregoing and other objects and advantages of the invention willappear from the following description. In the description reference ismade to the accompanying drawings which form a part hereof, and in whichthere is shown by way of illustration and not of limitation a preferredembodiment of the invention. Such embodiment does not represent the fullscope of the invention, but rather the invention may be employed in manydifferent embodiments, and reference is made to the claims herein forinterpreting the breadth of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENT FIG. I shows a Fourdrinier fabric 1 formed by joiningtogether the opposite ends of a woven length of the fabric along a seam2. The finished Fourdrinier fabric may have a width of up to 30 feet ormore, and the length along the loop of fabric may be as much as 180feet. The dimensions are dependent upon the particular pa permakingmachine for which the fabric is woven, and those given here are forillustrative purposes only. The upper side of the top half of the fabric1, as viewed in FIG. 1, is the papermaking side upon which a slurry ofpulp fibers is deposited at one end. The inner side of the fabric 1 isthe wear side and travels over and around machine rolls and suctionboxes, and in more modern machines foils in place of the small bed rollsthat were previously used. The fabric )1 is moved along at a substantialspeed and water drains through it to develop the fibers into an initialweb. By controlling the drainage and shaking the fabric in a crossmachine direction the fibers are oriented into random directions with asubstantial number becoming aligned in the cross machine direction, tothereby form the desired web which will ultimately have good strength inall directions. By

judicious positioning of the rolls, foils and suction boxes, the rate ofwater removal is controlled to facilitate this formation of a web.

FIG. 2 shows a portion of the wear surface of the fabric 1 on anenlarged scale, with the warp threads 3 running from the top to bottomof the figure. When the fabric 1 is made into a closed loop, as shown inFIG. 1, the warp threads 3 will extend around the loop, which is themachine direction, i.e. the direction in which the fabric 1 is movedover the rolls and other parts of the Fourdrinier machine. 7

The weft threads shown in FIG. 2 alternate in diameter between arelatively large weft 4 and a smaller weft 5. The warp threads 3, on theother hand, are of a uniform diameter throughout the fabric 1. The warpthreads 3 and weft threads 4, 5 are woven in a four shed weave of a1-2-3-4 pattern. Thus, for any group of four successive warp threads 3the first will pass beneath some selected weft, the second will passbeneath the next successive weft, the third will pass beneath the nextsuccessive weft, and the fourth will pass beneath the next successiveweft. This pattern develops a twill like effect. Four shed weaves arealso made in a satin pattern in which the warp threads are alternated inthe sequence 1-3-2-4, and in full twill weave in which each warp threadpasses over two and then under two weft threads, with successive warpsbeing staggered by a single weft thread.

Referring now to FIG. 3, there is shown a section along a warp thread 3which passes over two large weft threads 4 and a small weft thread 5,and then under a single small weft thread 5 in a repeated pattern. FIG.

4 shows a section along an adjacent warp thread 3 that passes over apair of small weft threads 5 and a single large weft thread 4, and thenbeneath a large weft thread 4 in a repeated pattern. In both FIGS. 3 and4 the papermaking side of the fabric 1 is at the top and the wear sideis at the bottom.

For the particular weave from which FIGS. 2-4 were taken the mesh countwas 79 warp threads per inch and 56 weft threads per inch. The warpdiameter was .20 mm, which is a typical warp diameter for normal fabricof this mesh count. The large diameter weft threads 4 had a diameter of.25 mm and the small diameter weft threads 5 had a diameter of .20 mm.These weft thread diameters compare with .22 mm which would be typicalfor this particular mesh count of 79 warp threads per inch and 56 weftthreads per inch. The large diameter wefts are increased over the normaldiameter approximately the same amount as the smaller wefts aredecreased in diameter from a normal value. Thus, the silhouette openarea of the embodiment being described is similar to that of ordinaryfabrics of the same mesh count. Tests of resistance to water drainageindi-' cate that fabrics of the invention should have similar bulkdrainage rates as usual fabrics of like mesh, and thus the novelintroduction of alternating weft diameter can be worked into Fourdrinierfabrics without material change in other weave parameters.

The warp threads 3 and weft threads 4 and 5 of the fabric of FIGS. 1-4are preferably of polyester material. As indicated hereinabove, othersynthetic materials are used for fabrics of this nature, and nylon,acrylics and copolymers are examples. Also, metal threads, coated metalthreads and combinations of these various materials may be feasible forimplementing the invention, so long as the uneven characteristic isdeveloped for the fabric surface.

FIGS. 3 and 4 are schematic, for some physical deformation of thethreads occurs under the highstresses of weaving, particularly in thevicinities of the crimps and knuckle formations, and these deformationsare not shown. These figures do indicate, however, that points along alarge diameter weft thread 4 are at a different level than correspondingpoints along a small diameter weft thread 5. Further, the warp knuckleson the bottom, or wear side, which pass under a small weft thread 5 areat a different level than the warp knuckles 7 that pass under a largeweft thread 4. Measurements have indicated that on the wear side of thefabric 1 some part of the knuckles of the large weft threads 4 form thelowermost points of the wear surface. They thus define the outer fabricsurface, and the limit of fabric thickness. Moving inward of the fabric1, or upward in FIGS. 3 and 4, the next thread surface encountered issome 7 part of the knuckles of the small diameter weft threads 5. Thenext higher thread surface recessed into the fabric 1 are the warpknuckles 7 that pass under large wefts 4. And recessed still furtherinto the fabric 1 are the warp knuckles 6 which pass under the smalldiameter weft threads 5. The relative levels in the fabric may vary fromthe results of the foregoing measurements, but as a result of thealternating weft thread diameters the wear surface of the fabric 1, asdefined by the individual thread levels in the fabric, is relativelyuneven or non-uniform.

A predominant amount of wear will be taken by the large diameter weftthreads 4 which have exposed long knuckles on the wear side. A smalleramount of wear will be taken by the small diameter weft threads 5, forthey are recessed and also present a smaller surface area. The warpthreads 3 will take wear at a later stage of fabric life. This shiftingof the wear in a large proportion to some of the weft threads mayaccount for'the long life of fabrics of the invention. Another factormay be that the uneven characteristic of the wear surface reduces thesuction effect on the fabric 1 as it rides over suction boxes and othermachine parts, so that the pressure of the fabric on box surfaces, andthe like, is reduced. As a result abrasive wear is reduced-and fabriclife increases. It also may be theorized that the water flow within thelower regions of the fabric 1 may be altered by the unevenness on thewear side such that the bottom surfaces of the threads are washed orretain a liquid film on their surface as they ride across a suction boxand other machine parts. There may be a resulting improved lubricationthat increases fabric life. In any event, the invention enhances fabricperformance.

By elevating the warp knuckle crests 6 and 7 into the fabric theresulting weave reduces the crimp in the warp knuckles. The resultingshallower warp knuckles will reduce the tendency of the warp threads 3to stretch under tension. Improved dimensional stability is therebyimparted to the fabric 1. The warp knuckles, however, remainsufficiently deep in curvature to adequately lock with the weft threads4, 5 so that an overly sleazy fabric is not developed.

The described embodiment introduces an uneven surface characteristicinto a Fourdrinier fabric by the use of alternating weft threaddiameters. In the practice of the invention it has been usual to reducethe diameter of the smaller wefts from the weft diameter of a normalweave, and to increase the diameter of the larger weft above that ofnormal weaves. While silhouette open areas are not materially affected,and drainage appears to remain the same as comparable prior fabrics,there is some increase in the total bulk of the weft 5 thread material.This may account to some extent for enhanced wear characteristics of thefabric.

The difference in the diameters of the large and the small weft threadsshould be at least 10 percent of the smaller of the two diameters. Thisdifference can extend upward to 50 percent, although for differentinstallations this upper limit may undoubtedly vary. For these ratios itis assumed that warp diameters will be held equal throughout the fabric.This need not, however, be a limitation in the practice of theinvention, nor should the specific weave be a limiting factor if thenon-uniform, or uneven surface characteristic is developed.

I claim:

1. In a Fourdrinier papermaking drainage fabric of interwoven warp andweft threads, the combination of:

a four shed weave pattern with both the warp threads and the weftthreads passing around one of the other threads on one side of thefabric and then around three of the other threads on the opposite sideof the fabric;

the warp threads being of substantially uniform diameter;

the weft threads being of an all synthetic material and alternating indiameter with every second thread being of a diameter larger than thealternate threads therebetween, the difference in weft thread diametersbeing at least 10 percent of the smaller weft thread diameter; and

crests of warp knuckles on the wear side of the fabric being recededwithin weft knuckle crests.

2. A papermaking fabric as in claim 1, wherein both the warp and weftthreads are of a synthetic monofilament material.

3. A papermaking fabric as in claim 1, wherein the diameter of the warpthreads is less than the values of the small and large weft threaddiameters.

4. A papermaking fabric as in claim 1, wherein the average surface levelof the smaller weft threads is receded into the fabric a greater degreethan the average level of the larger weft threads.

5. In a Fourdrinier papermaking fabric of interwoven warp and weftthreads that produce an open mesh for water drainage, the combinationof:

the warp and weft threads being woven in a repeated four shed patternand comprised of synthetic material;

adjacent weft threads varying in diameter with every other thread beingof larger diameter than the threads therebetween and with the minimumdifference in weft thread diameters being at least 10 percent of thesmallest weft thread diameter; and

60. the large diameter weft threads forming the outerthe fabric than theknuckles of the smaller diameter weft threads.

7. In a paperforming, drainage fabric of interwoven machine directionthreads and threads crosswise thereto, such threads being woven ofmonofilament, synthetic materials in a four shed weave, the combinationof:

said crosswise threads being composed of different diameter threads ofrelatively large diameter threads alternating with relatively smalldiameter threads;

the difference in diameter of the relatively large and relatively smallcrosswise threads being at least 10 percent of the smaller diameter;

threads.

1. In a Fourdrinier papermaking drainage fabric of interwoven warp and weft threads, the combination of: a four shed weave pattern with both the warp threads and the weft threads passing around one of the other threads on one side of the fabric and then around three of the other threads on the opposite side of the fabric; the warp threads being of substantially uniform diameter; the weft threads being of an all synthetic material and alternating in diameter with every second thread being of a diameter larger than the alternate threads therebetween, the difference in weft thread diameters being at least 10 percent of the smaller weft thread diameter; and crests of warp knuckles on the wear side of the fabric being receded within weft knuckle crests.
 2. A papermaking fabric As in claim 1, wherein both the warp and weft threads are of a synthetic monofilament material.
 3. A papermaking fabric as in claim 1, wherein the diameter of the warp threads is less than the values of the small and large weft thread diameters.
 4. A papermaking fabric as in claim 1, wherein the average surface level of the smaller weft threads is receded into the fabric a greater degree than the average level of the larger weft threads.
 5. In a Fourdrinier papermaking fabric of interwoven warp and weft threads that produce an open mesh for water drainage, the combination of: the warp and weft threads being woven in a repeated four shed pattern and comprised of synthetic material; adjacent weft threads varying in diameter with every other thread being of larger diameter than the threads therebetween and with the minimum difference in weft thread diameters being at least 10 percent of the smallest weft thread diameter; and the large diameter weft threads forming the outermost surface of the wear side, smaller diameter weft threads being recessed within this outermost surface, and warp knuckles on the wear side also being recessed within such outermost surface of the wear side.
 6. A papermaking fabric as in claim 5, with the warp knuckles on the wear side being recessed further within the fabric than the knuckles of the smaller diameter weft threads.
 7. In a paperforming, drainage fabric of interwoven machine direction threads and threads crosswise thereto, such threads being woven of monofilament, synthetic materials in a four shed weave, the combination of: said crosswise threads being composed of different diameter threads of relatively large diameter threads alternating with relatively small diameter threads; the difference in diameter of the relatively large and relatively small crosswise threads being at least 10 percent of the smaller diameter; said crosswise threads having the long knuckles thereof, that traverse more than one machine direction thread, being exposed on the wear side of the fabric; the average level of the long knuckles of said relatively small diameter crosswise threads being recessed within the relatively large diameter crosswise threads; and the knuckles of the machine direction threads being shallower than for the crosswise direction threads, and on the wear side being recessed within the knuckles of the relatively large diameter crosswise threads. 